Transmission method for cellular telephony mobile equipment&#39;s location data

ABSTRACT

A method of cellular telephony mobile equipment location based services data transmission utilizing an application which generates at least one message containing a set of data in a compressed format. The data set includes data from each particular message, specific data as to the message said, specific data as to measurements on Base Transceiver Stations or associated cells, and specific data on the cells monitored by the mobile equipment.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT/EP02/03592 filed 30 Mar.2002 and is based upon Italian national application TO2001A00029 of 30Mar. 2001 under the International Convention.

FIELD OF THE INVENTION

This invention relates to personal communication systems, such as, forexample, GSM operating standard communication systems, and specificallyrelates to a method for transmitting cellular mobile telephone locationdata.

BACKGROUND OF THE INVENTION

As is known, one of the possibilities offered by personal communicationsystems, such as the aforesaid GSM system, is the provision oflocation-based services, i.e. services based on determination of theposition of a mobile cellular telephone owner in an area served by oneor more Base Transceiver Stations (BTS).

This is possible because modern GSM mobile equipment s capable ofmeasuring Base Transceiver Stations in its own cell and neighboringcells, detecting, storing and transmitting the respective information.

This information comprises:

-   -   1. National code (Mobile Country Code=MCC) pertaining to the        serving cell;    -   2. Network code (Mobile Network Code=MNC) pertaining to the        serving cell;    -   3. Local area code (Local Area Code=LAC) pertaining to the        serving cell;    -   4. Serving cell identification (Cell ID);    -   5. Control channel signal intensity of serving cell (RxLev);    -   6. Control channel signal intensity of neighboring cells        detected by the telephone (RxLev);    -   7. Frequency indexes (BCCH-FREQ=Broad Control Channel-Frequency)        univocally corresponding to channel numbers (ARFCN=Absolute        Radio Frequency Channel Number) and identification codes        (BSIC=Base transceiver Station Identity Code) related to        neighboring cell base stations.

This information, consisting of numeric data, combined with thegeographic positions of the Base Transceiver Stations, contained in adatabase generally provided by the mobile telephone operator, can beused by an appropriate calculation procedure to estimate the position ofthe GSM mobile equipment.

The described information is normally tracked by the mobile equipmentvia a SIM Toolkit type application, installed on the SIM card(“Subscriber Identity Module”), and compressed to be sent by means ofSMS (Short Message System) messages to a remote Service Center.

Firstly, the received messages are decompressed and then fed into aprocessing system, called a “Location Engine”, which, by applying anappropriate algorithm, computes the geographical position of the mobileequipment. If required, the system either informs the mobile equipmentof its position or utilizes it for a location-based service.

The need to reduce the number of SMS messages transmitted for eachlocation request arises during the data exchange phase between mobileequipment and Service Center. This is necessary to satisfy the needs ofall mobile telephone operators, who cannot afford excessive traffic ontheir network for a single application, and of users, who requirecost-effectiveness.

Additionally, reducing the number of transmitted SMS text messages meanssignificantly reducing the response time of each location-based service,thus providing a significant contribution to service quality.

OBJECT OF THE INVENTION

It is the object of the invention to provide a cellular telephony mobileequipment location data transmission method which overcomes theseshortcomings and solves the described technical problems by implementinga compressed format for GSM mobile equipment location data suitable tobe sent in the form of an SMS message.

SUMMARY OF THE INVENTION

The invention is a method for transmitting cellular telephone mobileequipment location data in which an application, preferably installed ona SIM card contained in the mobile equipment, measures the BaseTransceiver Stations in the serving cell and the neighboring cells,detecting, storing and transmitting respective information to a remoteService Center by means of SMS messages, where a processing system,applying an appropriate algorithm and a Base Transceiver Stationsgeographic position database, computes the geographical position of themobile equipment and informs the mobile equipment of said geographicalposition.

The application preferably installed on the SIM card generates SMSmessages containing location data in compressed format, comprisingspecific data of each single message, specific data on the message set,specific data on measurements and specific data on the serving cell andthe neighboring cells monitored by the mobile equipment, the dimensionsof some data depending on the results of the measurements made at thecurrent instant and those obtained at an earlier time.

The location data in compressed format comprises:

for each message:

-   -   the current SMS message order number;    -   the total number of messages dedicated to location data        transmission;

consequently, in the message body:

-   -   data dedicated to specific services, where relevant;    -   the number of said measurements;

for each measurement:

-   -   RXLEV-FULL-SERVING-CELL, i.e. the intensity of is the serving        cell signal;    -   “Changed Tag”, i.e. the label indicating which of the four        data—Cell ID (serving cell identification), LAC (Local Area        Code), MCC (Mobile Country Code) and MNC (Mobile Network Code),        pertaining to the serving cell—have changed with respect to the        previous measurement;    -   MCC, if “Changed Tag” is higher than a first value;    -   MNC, if “Changed Tag” is higher than the first value;    -   LAC, if “Changed Tag” is higher than a second value;    -   Serving Cell ID, if “Changed Tag” is higher than a third value;    -   the number of monitored neighboring cells;

for each neighboring cell:

-   -   the relative intensity of the signal computed on the basis of        the previous measurement;    -   “ARFCN-BSIC cache index”, i.e. the index of the ARFCN-BSIC        (channel order number-identification code) pair in an        appropriate memory table;    -   ARFCN (channel order number), if “ARFCN-BSIC cache index” has a        first binary value;    -   BSIC (identification code), if “ARFCN-BSIC cache index” has the        first binary value; and    -   absolute intensity of the signal, if the “neighboring cell        relative signal intensity” has a second binary value.

The location data can have the following binary dimensions:

-   -   current SMS message order number, 4 bits;    -   total number of messages, 4 bits;    -   data dedicated to a specific service, 1 or more bytes;    -   measurement order number, 1 byte;    -   RXLEV-FULL-SERVICE-CELL, 6 bits;    -   “Changed Tag”, 2 bits;    -   MCC, 2 bytes;    -   MNC, 1 byte;    -   LAC, 2 bytes;    -   serving Cell ID, 2 bytes;    -   number of monitored neighboring cells, 1 byte;    -   neighboring cell signal relative intensity, 5 bits;    -   “ARFCN-BSIC cache index”, 3 bits;    -   ARFCN, 10 bits;    -   BSIC, 6 bits;    -   neighboring cell signal absolute intensity, 8 bits.

Whenever a new measurement is made, the application preferably installedon the SIM card checks which of the four data sets (Cell ID, LAC, MCCand MNC) have changed with respect to the previous measurement andconsequently sets the Changed Tag value, adding only the data which havechanged to the body of the SMS message.

In order to calculate the neighboring cell signal relative intensity,the application preferably installed on the SIM card uses a 1-bytememory table for each monitored neighboring cell and, during SMS coding,initializes a third binary value for each item in the table and carriesout the following operations after each neighboring cell signalintensity measurement:

-   -   if the intensity of the current neighboring cell is included in        a first binary range with respect to the intensity of the        previous measurement related to the neighboring cell in the same        position, the application only transmits the difference between        the intensities and updates the table with the current intensity        absolute value;    -   otherwise the second binary value is assigned to the relative        intensity, the absolute current intensity value is sent in the        subsequent byte and the table is updated with the same absolute        value,

a similar reversed procedure being carried out on Service Center sidefor decoding.

The application preferably installed on the SIM card uses a table formedby pairs of ARFCN-BSIC values which are filled progressively as newARFCN-BSIC pair values are encountered to obtain said “ARFCN-BSIC cacheindex”, and

-   -   if a value present in the table is encountered, the ARFCN-BSIC        pair line order number or index containing the encountered value        is used instead of the value itself;    -   if an ARFCN-BSIC value which is not present in the table is        encountered and the table is full, the new value will be written        over the oldest, according to FIFO mode, while, if the table is        not fill, “ARFCN-BSIC cache index” is set to the first binary        value and the real value is added in the subsequent bytes,        whereby adding the new value in the table,

a similar reversed procedure being carried out on the Service Centerside for decoding.

BRIEF DESCRIPTION OF THE DRAWING

Additional characteristics and advantages of the invention will now bedescribed by way of example only, with reference to the accompanyingdrawing in which:

FIG. 1 is a diagram of the network and serving cell data formataccording to GSM standard;

FIG. 2 is a diagram of the signal intensity of all monitored cells,frequencies and identification codes of neighboring cells;

FIG. 3 is a diagram of the channel number format of the neighboring celllinks;

FIG. 4 is a diagram of the first byte in the message according to theinvention;

FIG. 5 is a diagram of the service data and measurement number format,where relevant;

FIG. 6 is a diagram of the data format of each measurement; and

FIG. 7 is a diagram of the data format of each neighboring cell.

SPECIFIC DESCRIPTION

The Base Transceiver Stations data format measured by the mobileequipment and supplied to its SIM card is described in GSMspecifications and essentially concerns three different types of data:

-   -   Data on the network and serving cell currently in use, indicated        as MCC, MNC, LAC and Cell ID in the description above. Numeric        representation is illustrated in FIG. 1.    -   Data on signal intensity in monitored cells, frequency index and        neighboring cell identification codes, indicated as RxLev,        BCCH-FREQ and BSIC in the description above. Numeric        representation, defined in GSM 04.08 specifications, is        illustrated in FIG. 2.    -   List of neighboring cell link channel number, indicated as ARFCN        in the description above. Numeric representation, defined in GSM        11.14, specifications, is illustrated in FIG. 3.

As shown in FIG. 1, MCC, LAC and Cell ID are each represented by twobytes, High Byte and Low Byte, while MNC only requires one.

FIG. 2 shows data on signal intensity, frequencies, codes, etc.,pertaining to neighboring cells, distributed on 17 octets (or bytes),for up to eight monitored cells.

Specifically, the fields have the following meaning in GSM context:

-   -   Measurement Results IEI (7 bits): identifier of the information        that follows (IEI=Information Element Identifier), i.e.        measurement results in this case;    -   BA-USED (1 bit): BCCH coding type;    -   DTX-USED (1 bit): indicating whether the mobile equipment uses        DTX (DTX=Discontinuous transmission [mechanism]) or not, i.e. a        power level transmission which is not continuous in the previous        measurement period;    -   RXLEV-FULL-SERVING-CELL (6 bits): intensity of the signal        received from the serving cell, measured on all slots;    -   MEAS-VALID (1 bit): indicating validity of measurements on the        dedicated channel;    -   RXLEV-SUB-SERVING-CELL (6 bits): intensity of the signal        received from the serving cell, measured on a subset of slots;    -   RXQUAL-FULL-SERVING-CELL (3 bits): quality of the signal        received from the serving cell measured on all slots;    -   RXQUAL-SUB-SERVING-CELL (3 bits): quality of the signal received        from the serving cell measured on a subset of slots;    -   NO-NCELL-M (3 bits): number of measurements of neighboring        cells;    -   RXLEV-NCELL I (6 bits): intensity of signal received from the        i-th neighboring cell (I=1 . . . 6);    -   BCCH-FREQ-NCELL I (5 bits): frequency index related to the BCCH        channel of the i-th neighboring cell;    -   BSIC-NCELL I (6 bits): identification code of the i-th        neighboring cell base station.

FIG. 3 illustrates the link frequency format, identified as the absolutenumber of the m-th radio-frequency channel (ARFCN#m). Each is formed byten consecutive bits, subdivided into “high part” and “low part”, andidentified by said frequency index BCCH-FREQ-NCELL I.

Sending all this information in standard GSM format would be rathercostly in terms of the number of SMS messages required. This is becausethe mobile equipment must provide a certain number of consecutivemeasurements for sufficiently accurate and reliable location to filterdetected signal frequency peaks (positive and negative).

According to the invention, the transmission of location data detectedby the GSM equipment is made using a compressed format which requires avery reduced number of SMS messages. Naturally the number of SMSmessages will be effected, since accuracy and reliability of locationdepends on the number of measurements made.

Generation of said format must be as simple as possible because it isprocessed by a SIM card application and, as known, the SIM cardperformance and computing capacity are poor if compared to those of apersonal computer. Furthermore, a complex application would occupy agreat deal of memory space, consequently penalizing optionallocation-based services, which are interesting from a commercial pointof view.

The application installed on the SIM card generates SMS messagescontaining location data in compressed format, comprising specific dataon each single message, specific data on the message set, specific dataon measurements and specific data on the serving cell and theneighboring cells monitored by the mobile equipment. The dimensions ofsome data depend on the results of the measurements made at the currentinstant and those obtained at an earlier time.

The format description refers to FIGS. 4, 5, 6 and 7 which illustratestables in which each line corresponds to a byte in the SMS message.

Considering that the aforesaid information can occupy more than one SMSmessage, the first byte of each message must contain the data shown inFIG. 4, i.e. the current SMS message number and the total number ofmessages dedicated to location data transmission.

The subsequent bytes in the body of the message contain informationdescribed in FIG. 5. Specifically, some bytes are dedicated to “possibleservice-specific data”, i.e. data dedicated to a specific service. Thisis because the mobile equipment location process could be linked to highnumber of location-based services installed on the user's SIM card. Inthese cases, numerous other data may need to be communicated to theService Center. For example, transmission may include the selection theuser made in a telephone menu (SAT application). Such data must beincluded in the transmitted SMS messages and integrated with purelocation information.

An additional byte is used to indicate the number of measurements.

FIG. 6 lists the data transmitted for each measurements, particularly:

-   -   RXLEV-FULL-SERVING-CELL (6 bits), i.e. the intensity of the        serving cell signal;    -   “Changed Tag” (2 bits), whose meaning is explained below;    -   MCC (2 bytes, High byte and Low byte), present if the “Changed        Tag” is higher than 2;    -   MNC (1 byte), present if “Changed Tag” is higher than 2;    -   LAC (2 bytes, High byte and Low byte), present if “Changed Tag”        is higher than 1;    -   Serving Cell ID (2 bytes, High byte and Low byte), present if        “Changed Tag” is higher than 0;    -   the number of monitored neighboring cells (1 byte).

“Changed Tag” is useful when several consecutive measurements arerequired by the mobile equipment. This condition is necessary to obtainreliable locations. “Changed Tag” indicates which of the four cell data(Cell ID, LAC, MCC or MNC), related to the serving cell, have changedwith respect to the previous measurement. When a new measurement ismade, the procedure checks what has changed with respect to the previousdata stored by the SIM card and sets the Changed Tag value consequently.Finally, only the data which have changed are added to the SMS messagebody.

The data listed in FIG. 7 are measured and transmitted for eachneighboring cell, specifically:

-   -   the relative intensity of the neighboring cell signal (5 bits),        computed on the previous measurements as explained below;    -   “ARFCN-BSIC cache index” (3 bits), whose meaning will be        explained below;    -   ARFCN (10 bits), subdivided into two parts, one consisting of        one byte and one by two bits. Present if “ARFCN-BSIC cache        index” has binary value “111”;    -   BSIC (6 bits), also present if “ARFCN-BSIC cache index” has        binary value “111”; and    -   absolute intensity of neighboring cell signal (8 bits), present        if the relative intensity of the neighboring cell has binary        value “11111”.

The application residing on the SIM card uses a 6-byte memory table tocompute the relative intensity of the neighboring cell signal, one foreach monitored neighboring cell. During SMS message coding, each elementof the table is initialized to binary value “11110”. Subsequently, thefollowing operations are carried out each time the neighboring cellsignal is detected:

-   -   if the intensity of the current neighboring cell is included in        the binary range ±“01111” with respect to the intensity of the        previous measurement related to the neighboring cell in the same        position, only the difference in intensity is transmitted        (therefore only 5 bits in the SMS message are required) and the        table is updated with the absolute value of the current        intensity;    -   otherwise the binary value “11111” is assigned to the relative        intensity, the absolute current intensity value is sent in the        subsequent byte and the table is updated with the same absolute        value.

A similar reversed procedure is carried out on Service Center side fordecoding.

“ARFCN-BSIC cache index” is the index of the ARFCN-BSIC pair in aspecific memory table (cache). The pair is used to determine the Cell IDwhich univocally identifies the neighboring cell.

It is very likely for the set of monitored neighboring cells to changesignificantly during multiple consecutive measurements required forcorrect location. Consequently, a specific table is used to reduce thespace required to store the ARFCN-BSIC pairs related to monitoredneighboring cells. This table has a capacity of seven value pairs and isfilled progressively as new ARFCN-BSIC pair values are found.

If a value present in the table is encountered, the row number, orindex, containing the encountered value is used instead of the valueitself. A considerable amount of space is saved since the index onlyoccupies 3 bits, while the ARFCN-BSIC pair occupies 16 bits.

If an ARFCN-BSIC value which is not present in the table is encounteredand the table is full, the new value will be written over the oldest,according to FIFO mode. This mechanism ensures high simplicity inmanagement and good efficiency. “ARFCN-BSIC cache index” is set tobinary “111” and the real value is added in the subsequent bytes asshown in the format specifications when an ARFCN-BSIC pair value whichis not present in the table is encountered. The new value is thus addedto the table.

A similar reversed procedure is carried out on Service Center side fordecoding.

Naturally, numerous changes can be implemented to the construction andembodiments of the invention herein envisaged without departing from thescope of the present invention, as defined by the following claims.

1. A method of cellular telephony mobile equipment location basedservices data transmission, in which an application carries outmeasurements on Base Transceiver Stations or associated cells bydetecting, storing and transmitting respective information to a remoteService Center by means of messages, where a processing system applyingcalculation procedures and a Base Transceiver Stations geographicposition database compute data associated to the location basedservices, the method comprising: generating in the application at leastone message containing a set of data in compressed format, the set ofdata being selected from a set comprising specific data on each singlemessage, specific data on the message set, specific data on themeasurements and specific data on the cells monitored by the mobileequipment, said data in compressed format comprising: for each message:a current message order number; and a total number of messages dedicatedto location based services data transmission; in the message body: datadedicated to specific services; and/or a number of said measurements;for each measurement: RXLEV-FULL-SERVING-CELL data representing anintensity of a signal of the serving cell associated with said mobileequipment; a “Changed Tag” label indicating which of the data: Cell IDserving cell identification, LAC Local Area Code, MCC Mobile CountryCode and MNC Mobile Network Code, associated to the Changed Tag labeland pertaining to the serving cell have changed with respect to aprevious measurement; MCC, if “Changed Tag” is higher than a firstvalue; MNC, if “Changed Tag” is higher than the first value; LAC, if“Changed Tag” is higher than a second value; Serving Cell ID, if“Changed Tag” is higher than a third value; and a number of monitoredneighboring cells associated with the mobile equipment; for eachneighboring cell: a relative intensity of the signal computed on thebasis of a previous measurement; an “ARFCN-BSIC cache index” of theARFCN-BSIC channel order number-identification code pair in a memorytable; an “ARFCN channel order number, if “ARFCN-BSIC cache index” has afirst binary value; a BSIC identification code if “ARFCN-BSIC cacheindex” has the first binary value; and an absolute intensity of thesignal, if the neighboring cell relative signal intensity” has a secondbinary value.
 2. Method according to claim 1 wherein said data incompressed format have the following binary dimensions: current messageorder number, 4 bits; total number of messages, 4 bits; data dedicatedto a specific service, 1 or more bytes; measurement order number, 1byte; RXLEV-FULL-SERVICE-CELL, 6 bits; “Changed Tag”, 2 bits; MCC, 2bytes; MNC, 1 byte; LAC, 2 bytes; serving Cell ID, 2 bytes; number ofmonitored neighboring cells, 1 byte; neighboring cell signal relativeintensity, 5 bits; “ARFCN-BSIC cache index”, 3 bits; ARFCN, 10 bits;BSIC, 6 bits; and neighboring cell signal absolute intensity, 8 bits. 3.The method according to claim 2 wherein whenever a new measurement ismade, said application checks which of the data Cell ID, LAC, MCC andMNC associated to the Changed Tag label have changed with respect to theprevious measurement and consequently sets the Changed Tag label, addingonly the corresponding data which have changed to the body of themessage.
 4. The method according to claim 2 wherein in order tocalculate said neighboring cell signal relative intensity, saidapplication uses a 1-byte memory table for each monitored neighboringcell and, during message coding, initializes a third binary value foreach item in the table and carries out the following operations aftereach neighboring cell signal intensity measurement: if an intensity ofthe current neighboring cell is included in a first binary range withrespect to the intensity of the previous measurement related to theneighboring cell in the same position, the application only transmitsthe difference between the intensities and updates the table with thecurrent intensity absolute value; and otherwise the second binary valueis assigned to the relative intensity, the absolute current intensityvalue is sent in the subsequent byte and the table is updated with thesame absolute value, a reversed procedure being carried out at theService Center for decoding.
 5. The method according to claim 2 whereinsaid application uses a table formed by pairs of ARFCN-BSIC values whichare filled progressively as new ARFCN-BSIC pair values are encounteredto obtain said “ARFCN-BSIC cache index”, and if a value present in thetable is encountered, the ARFCN-BSIC pair line order number or indexcontaining the encountered value is used instead of the value itself;and if an ARFCN-BSIC value which is not present in the table isencountered and the table is full, the new value will be written overthe oldest, according to FIFO mode, while, if the table is not fill,“ARFCN-BSIC cache index” is set to the first binary value and the realvalue is added in the subsequent bytes, whereby adding the new value inthe table, a reversed procedure being carried out at the Service Centerfor decoding.
 6. The method according to claim 1 wherein said at leastone message containing a set of data in compressed format is a SMS typemessage.
 7. The method according to claim 1 wherein said application isinstalled on the mobile equipment or on a SIM card contained in themobile equipment.
 8. The method according to claim 1 wherein saidprocessing system informs the mobile equipment of said geographicalposition.
 9. The method according to claim 1 wherein said data incompressed format comprise service specific data dedicated to a specificservice.